There have conventionally been proposed various thermal printers which are provided with a thermal head on which a plurality of heater elements are arranged, and configured to perform printing by selectively controlling energization of each heater element. In the thermal printers, it is selectively controlled whether to energize or de-energize each of the plurality of heater elements according to printing data, so as to heat up the plurality of heater element. Such thermal printers generate heat at heater elements so as to heat heat-sensitive paper and form colors thereon, or to transfer a thermal fusion ink, for performing printing according to the printing data.
As described above, a thermal printer performs printing by generating heat at heater elements; then, the thermal head and the heater elements gradually store heat as the printing proceeds. The printing cycle at the thermal printer consists of heating period for heating up the heater elements and non-heating period for dissipating heat in the heater elements, but if heat is stored above dissipating ability of the thermal head in the thermal head or the heater elements, it may adversely affect the sensitivity of the heat-sensitive paper or the melting of the ink, resulting in highly dark printing. Also, this sometimes causes collapse, trailing or uneven density in printed materials, deteriorating the printing quality.
There has been known a thermal printer configured to address the above problem. The thermal printer prevents the occurrence of uneven density in the printed materials by controlling the energy of an energization pulse to apply to the thermal head, on the basis of the temperature in the vicinity of the thermal head.
In the field of the above thermal printers, there has been desired high-speed printing to reduce the print time. In addition, even if the print cycle becomes short for coping with the high-speed printing, sufficient energy should be secured for printing. In a case where the energy amount of energization pulse is controlled as in the thermal printer, voltage-resistant components or components with improved capacitance have to be used in the thermal head, etc. and this drives up the cost.
If the printing cycle is shortened, the proportion of a heating period in the printing cycle increases. Thereby, a non-heating period is shortened in the printing cycle at the time of high-speed printing. As a result, the time period for dissipating the heat from the thermal head and heater elements is also shortened, and the thermal head becomes apt to store heat, causing collapse, trailing or uneven density in printed materials, and resulting in considerably degrading the printing quality.